(a) Field of the Invention
The present invention relates to a smelting reduction system, more particularly, to a fluidized bed reactor which supplies reduced iron to a melter-gasifier.
(b) Description of the Related Art
Generally, a blast furnace has been extensively used to make a molten iron through reducing and melting an iron ore. However, the blast furnace involves a drawback in that the charging materials should suffer pre-treatment to bear the form of sintered iron ore or cokes.
In order to solve such a problem, a fluidized bed reduction technique has been developed with the direct use of fine iron ore and coal without pre-treatment. U.S. Pat. No. 4,978,387 discloses such a technique in a typical manner.
The fluidized bed reduction technique disclosed therein is roughly based on a melter-gasifier and a fluidized bed reduction reactor. The melter-gasifier gasifier the coal charged therein to make a reduction gas, and melts the reduced iron fed from the fluidized bed reduction reactor. The fluidized bed reduction reactor utilizes the reduction gas generated from the melter-gasifier to reduce an iron ore in an indirect manner. The fluidized bed reduction reactor is provided with a pre-heating furnace for pre-heating the iron ore charged therein, a pre-reduction furnace for reducing the iron ore fed from the pre-heating furnace, and a final reduction furnace.
In operation, an iron ore is charged into the pre-heating furnace, and heated therein. The iron ore is then reduced while passing through the pre-reduction furnace and the final reduction furnace. The reduction gas generated from the melter-gasifier is sequentially flown into the final reduction furnace, the pre-reduction furnace, and the pre-heating furnace. It can be easily known that the flowing direction of the reduction gas is directly opposite to that of the iron ore. The reduced iron ore is continuously fed into the melter-gasifier where a deposit of coal is formed, and melt at the deposit to thereby make a molten iron.
The fluidized bed reduction reactor can be classified into a moving bed type and a fluidized bed type according to the state of contact between the iron ore and the reduction gas therein. Considering that the iron ore to be reduced has fine particles widely distributed in size, it can be known that the fluidized bed type is effectively employed for use in reducing the fine iron ore. The fluidized bed type refers to the technique where the reverse-current reduction gas is fed to a distribution plate provided at the bottom of each reduction furnace as a gas distributor, and reduces the iron ore charged therein while fluctuating the fine ore particles falling from the top side.
As the fluidized bed reduction furnace forms a fluidized bed through mixing the iron ore particles with the reverse-current reduction gas therein, the production efficiency largely depends upon the flowing state of the fine iron ore along the serially arranged furnaces, and the supply state of the reverse-current reduction gas.
In particular, when the reduction gas containing a large amount of dust passes through the nozzle of each distribution plate, the dust components may be gradually accumulated there. As a result, the non-fluidized iron ore particles drop to the bottom and clog the nozzle. In case the nozzle of the distribution plate is clogged, the flow of the reduction gas is blocked at the nozzle while deteriorating the working conditions in a serious manner.
Meanwhile, raw coal is combusted and gasified at the melter-gasifier to produce reduction gas, and the resulting reduction gas is differentiated in quantity depending upon the content and producing districts of the raw coal, and the working conditions. It has been noted that radical variation in the amount of the reduction gas product may reach up to 20-30% of the average quantity. Such a radical variation occurring for an extremely short time period is usually called the xe2x80x9cpressure peak.xe2x80x9d
When such a pressure peak occurs in the fluidized bed reduction process, the amount of high temperature reduction gas fed to the respective fluidized bed reduction furnaces radically increases within a short time, and again, radically decreases.
When the amount of high temperature reduction gas radically increases with the occurrence of pressure peak, the amount of reduction gas fed to the respective reduction furnaces as well as to the gas supply lines interconnecting the furnaces also increases in a radical manner. Consequently, the large amount of reduction gas is flown along the lines in a high velocity while blocking the reverse-current iron ore flux. In a serious case, the iron ore flux may proceed in the opposite direction. Such a blockage of the iron ore flux is sustained for a relatively long time even after the pressure peak is extinguished away. This deteriorates the working conditions at the fluidized bed reduction reactor, and induces serious device failure.
Furthermore, in case the amount of high temperature reduction gas radically decreases with the occurrence of pressure peak, the flowing speed of the reduction gas also radically decreases so that the fluidized iron ore bed in each furnace may be temporarily broken. When the fluidized bed is broken, the fine iron ore particles broken away from the fluidized bed are gradually accumulated on the distribution plate placed at the bottom of the furnace while clogging the diffusion nozzle.
As described above, in order to make fluent working conditions in the fluidized bed reduction reactor, it is necessary that the reduction gas should be uniformly supplied thereto in a predetermined velocity while making the fluidized bed in a stable manner.
However, in the conventional fluidized bed reduction reactor, technical difficulties are involved in preventing blockage of the flow of the reduction gas or the iron ore, or the breakage of the fluidized bed.
It is an object of the present invention to provide a fluidized bed reduction reactor which can sustain the flow of iron ore and reduction gas in a stable manner.
It is another object of the present invention to provide a fluidized bed reduction reactor which can form a normal fluidized bed while ensuring the fluent flow of iron ore.
It is still another object of the present invention to provide a fluidized bed breakage prevention unit which can prevent temporary breakage of the fluidized bed with decrease in the reduction gas.
It is still another object of the present invention to provide an iron ore flow blockage prevention unit which can prevent blockage of the iron ore flux with the occurrence of pressure peak.
It is still another object of the present invention to provide a nitrogen gas supply unit which can supply nitrogen gas to the bottom of each fluidized bed reduction furnace through sensing the pressure difference and the temperature change therein.
These and other objects may be achieved by a fluidized bed reduction reactor for reducing fine iron ore and supplying the reduced iron ore to a melter-gasifier. The fluidized bed reduction reactor includes at least two or more fluidized bed furnaces pre-heating, pre-reducing, and finally reducing the charged fine iron ore with a reduction gas supplied from the melter-gasifier in a sequentially manner. A scrubber receives an exhaust gas from the pre-heating furnace via an exhaust tube, cools the exhaust gas, and scrubs fine particles contained in the exhaust gas. At least two or more iron ore discharge tubes inter-communicate the fluidized bed furnaces, and inter-communicate the final reduction furnace and the melter-gasifier to discharge the charged iron ore to the subsequent furnace or the melter-gasifier. At least two or more reduction gas supply tubes inter-communicate the fluidized bed furnaces, and inter-communicate the final reduction furnace and the melter-gasifier to supply the reduction gas generated from the melter-gasifier to each fluidized bed furnace. A fluidized bed stabilization unit stabilizes the fluidized bed when the fluidized bed in each fluidized bed furnace is broken due to the unstable supply of the reduction gas from the bottom.
The fluidized bed stabilization unit includes an exhaust gas supply unit. The exhaust gas supply unit supplies the exhaust gas to the reduction gas supply tube interconnecting the melter-gasifier and the fluidized bed reduction furnaces at the time point when the pressure of the reduction gas within the fluidized bed reduction furnaces radically decreases with the occurrence of pressure peak.
The fluidized bed stabilization unit may further include an iron ore flow blockage prevention unit. The iron ore flow blockage prevention unit directly bypasses some of the reduction gas from each iron ore discharge tube disposed between the neighboring furnaces to the scrubber at the time point when the inner pressure of the melter-gasifier radically increases with the occurrence of pressure peak.
The fluidized bed stabilization unit may still further include a backup gas supply unit. The backup gas supply unit supplies a backup nitrogen gas to the bottom of each fluidized bed reduction furnace when a nozzle of a distribution plate provided at the bottom of the fluidized bed reduction furnace is clogged.
The components of the fluidized bed stabilization unit may be provided in a separate manner, or in a combinatorial manner.
In order to stabilize the fluidized bed in each fluidized bed furnace, each iron ore discharge tube interconnecting the neighboring furnaces is intercepted at an initial working state. A fluidized bed is formed within each fluidized bed furnace through blowing the reduction gas into the furnace from the bottom, and charging the fine iron ore into the furnace from the top. The fluidized bed is grown in height such that the highest portion of the fluidized bed is placed at the same plane as the inlet of the corresponding iron ore discharge tube. The iron ore discharge tube is gradually opening the iron ore discharge tube after the fluidized bed is stabilized.
In the case of breakage of the fluidized bed, the fluidized bed stabilization unit is operated to recover and stabilize the broken fluidized bed.
In this way, the fluidized bed reactor can be operated for a long time in a stable manner, significantly enhancing production efficiency.